Abominations are captured human test subjects whose bodies have been hybridized with alien DNA with the intention of creating biological weapons. The transformation process turns the subjects into feral, half human, half-alien menacing creatures that are hostile to anything that is not one of them,[Non-canon 1][Non-canon 2] including their alien creators. It also removes all discernible sexual characteristics, leaving them with an androgynous appearance. Despite this, it is evident that these creatures retain some degree of their humanity and self-awareness. When killing an abomination, sometimes they say "thank you" as if to suggest that they had wanted to die all along.
Their known creation history and asexual appearance seem very similar to super mutants, while their hostility and lack of self-preservation are reminiscent of feral ghouls.
After spotting a target, an abomination will point at it and wail loudly, and then attack with its long arms (in a manner that is very similar to feral ghouls), making them difficult to engage with unarmed or melee weapons. Abominations are a fairly standard opponent and are easily killed with alien weapons. When killed, their bodies often contain various conventional alien items, such as alien power modules or alien epoxy. Sometimes, however, they contain items commonly found on the bodies of feral ghouls, such as packs of cigarettes, pre-War money, harmonicas and other miscellaneous items, which serve to reinforce the abominations' human origin. In a few rare cases, they can also have pre-War books.
Upon being killed, an abomination can sometimes be heard saying "thank you," indicating that it wanted to die. The Pitt's trogs also sometimes utter the same remark when dying. However, no change in Karma results from killing one.
The way that the abominations point and screech when they notice the player character is a reference to the 1978 remake of the movie Invasion of the Body Snatchers, in that the alien "pod-people" point and screech in the same way whenever they discover a real human.
↑Fallout 3 Official Game Guide Game of the Year Edition p. 728: "The true horror of the Aliens’ abduction begins to sink in as you discover the more grisly side of their probing. This series of chambers is dotted with the corpses of those of particular interest to these fiends, along with the Aliens’ greatest triumph: half-human, half-Alien hybrids known only (and suitably) as Abominations."
↑Fallout 3 Official Game Guide Game of the Year Edition p. 714: "Dear god, what abominations are these?! Oh right, that’s exactly what they are. These half-human hybrids can’t be reasoned with."